Optical disk medium and method and apparatus for reading information

ABSTRACT

An optical disk medium includes a track groove thereon. On the optical disk medium, information is recorded along the track groove on a block unit basis. The block unit has a predetermined length. The block unit having the predetermined length includes a number of sub-blocks that are arranged along the groove. A sub-block mark is provided within each of the sub-blocks and used to identify the sub-block.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is continuation of Co-pending U.S. patent applicationSer. No. 12/015,081, which was a divisional of U.S. patent applicationSer. No. 11/265,688 filed No. Nov. 2, 2005, now U.S. Pat. No. 7,362,664,issued Apr. 22, 2008, which was a continuation of U.S. patentapplication Ser. No. 10/796,874 filed Mar. 9, 2004, now U.S. Pat. No.7,116,630, issued Oct. 3, 2006, which was a divisional of U.S. patentapplication Ser. No. 10/173,903, filed Jun. 17, 2002, now U.S. Pat. No.6,724,708, issued Apr. 20, 2004, the disclosures of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical disk on which information(e.g., digital video information) can be stored at a high density.

2. Description of the Related Art

In recent years, the recording density of optical disk media goes onincreasing. On an optical disk medium on which data or information canbe written by a user, a track groove has normally been formed in advanceand a recording film has been formed so as to cover the track groove.Data or information is written by the user on the recording film alongthe track groove, i.e., either on the track groove or on an area (land)interposed between adjacent parts of the track groove.

The track groove is formed so as to wobble just like a sine wave and aclock signal is generated in accordance with a wobble period.Synchronously with this clock signal, user data is written on, or readout from, the recording film.

To write data at a predetermined location on an optical disk, addressinformation (or location information), indicating physical locations onthe optical disk, needs to be allocated to, and recorded at, respectivesites on the optical disk while the disk is being manufactured.Normally, an address is allocated to a series of areas that are arrangedalong a track groove and have a predetermined length. There are variousmethods for recording such address information on an optical disk.Hereinafter, a conventional method for recording an address on anoptical disk will be described.

Japanese Laid-Open Publication No. 6-309672 discloses a disk storagemedium on which a wobbling track groove is discontinued locally so thatan address-dedicated area is provided for the discontinued part.Pre-pits, representing address information recorded, are formed on theaddress-dedicated area on the track groove. This optical disk has astructure in which the address-dedicated area and a data-dedicated area(for writing information thereon) coexist on the same track groove.

Japanese Laid-Open Publication No. 5-189934 discloses an optical disk onwhich address information is recorded by changing the wobble frequencyof a track groove. In an optical disk like this, an area on which theaddress information is recorded and an area on which data will bewritten are not separated from each other along the track.

Japanese Laid-Open Publication No. 9-326138 discloses an optical disk onwhich prepits are formed between adjacent parts of a track groove. Thesepre-pits represent the address information recorded.

These various types of optical disks have the following problems to besolved for the purpose of further increasing the recording density.

First, as for the optical disk on which address information is recordedas pre-bits within the address-dedicated area on the track, a so-called“overhead” occurs to secure the address-dedicated area, and the dataarea should be reduced for that purpose. As a result, the storagecapacity available for the user has to be reduced.

Next, as for the optical disk for recording an address thereon bymodulating the wobble frequency of the track, a write clock signalcannot be generated precisely enough. Originally, the wobble of thetrack groove is created mainly to generate a clock signal forestablishing synchronization required for read and write operations.Where the wobble frequency is unique, a clock signal can be generatedhighly precisely by getting a read signal, having amplitude changingwith the wobble, synchronized and multiplied by a PLL, for example.However, if the wobble frequency is not unique but has multiplefrequency components, then the frequency band that the PLL can follow upshould be lowered (as compared to the situation where the wobble has aunique frequency) to avoid pseudo locking of the PLL. In that case, thePLL cannot sufficiently follow up the jitter of a disk motor or a jitterresulting from the eccentricity of a disk. Thus, some jitter mightremain in the resultant recording signal.

On the other hand, where the recording film formed on the optical diskis a phase-change film, for example, a signal read out from such arecording film may have a decreased SNR if data is overwritten on thefilm repeatedly. If the wobble frequency is unique, the noise componentsare removable using a bandpass filter having a narrow band. However, ifthe wobble frequency has been modulated, the filter should have itsbandwidth broadened. As a result, the noise components are much morelikely contained and the jitter might be further worsened. It isexpected that the recording density will be further increased from nowon. However, the higher the recording density, the narrower theallowable jitter margin will become. Accordingly, it will be more andmore necessary to minimize the increase of jitter by avoiding themodulation of the wobble frequency.

In the structure in which the pre-pits representing the addressinformation recorded are formed between adjacent parts of the groove, itis difficult to form long enough pre-pits in sufficiently large numbers.Accordingly, as the recording density is increased, detection errorsmight increase its number. This is because if large pre-pits are formedbetween adjacent parts of the groove, then those pits will affectadjacent parts of the track.

BRIEF SUMMARY OF THE INVENTION

In order to overcome the problems described above, a main object of thepresent invention is to provide an optical disk medium that contributesto minimizing the overhead and generating a clock signal preciselyenough in accordance with the wobble of the track groove.

Another object of this invention is to provide a method and apparatusfor reading an address that has been recorded on the optical diskmedium.

An optical disk medium according to the present invention includes atrack groove thereon. On the optical disk medium, information isrecorded along the track groove on a block unit basis. The block unithas a predetermined length. The block unit includes a number ofsub-blocks that are arranged along the groove. A sub-block mark isprovided within each said sub-block and used to identify the sub-block.

In one preferred embodiment of the present invention, the track grooveis preferably provided with a periodic wobble, and the sub-block mark ispreferably formed by locally changing the phase of the wobble.

In another preferred embodiment of the present invention, the trackgroove is preferably provided with a periodic wobble, and the sub-blockmark is preferably provided with a wobble having a frequency differentfrom that of the other parts of the track groove.

In still another preferred embodiment, the wobble of the track groovepreferably has a shape that represents address information of the blockunit.

In this particular preferred embodiment, the wobble of the track groovepreferably has a sawtooth shape that represents the address informationof the block unit.

Alternatively or additionally, the information represented by the wobbleshape of the track groove is preferably also represented by thesub-block.

The present invention provides a method for reading address informationfrom the optical disk medium of the present invention. The methodincludes the step of generating a first sync signal and multiplying thefirst sync signal and a read signal together to obtain a first product.The read signal has been detected in accordance with the wobble of thetrack groove and has a basic frequency. The first sync signal issynchronized with the read signal and has a frequency that is equal tothe basic frequency of the read signal. The method further includes thestep of generating a second sync signal and multiplying the second syncsignal and the read signal together to obtain a second product. Thesecond sync signal is synchronized with the read signal and has afrequency that is twice as high as the basic frequency of the readsignal. The method further includes the steps of: integrating the firstand second products to obtain an integral; and comparing the integralwith a predetermined threshold value, thereby defining the addressinformation.

The present invention further provides an apparatus for reading addressinformation from the optical disk medium of the present invention. Theapparatus includes first multiplier, second multiplier, integratingmeans and comparing means. The first multiplier multiplies a first syncsignal and a read signal together. The read signal has been detected inaccordance with the wobble of the track groove and has a basicfrequency. The first sync signal is synchronized with the read signaland has a frequency that is equal to the basic frequency of the readsignal. The second multiplier multiplies a second sync signal and theread signal together. The second sync signal is synchronized with theread signal and has a frequency that is twice as high as the basicfrequency of the read signal. The integrating means integrates outputsof the first and second multipliers. And the comparing means compares anoutput value of the integrating means with a predetermined thresholdvalue, thereby defining the address information.

Another optical disk medium according to the present invention includesa track groove thereon. On the optical disk medium, information isrecorded along the track groove. The track groove includes a number ofunit sections that are arranged along the track groove and that haveside faces displaced periodically along the track groove. Subdividedinformation is allocated to each said unit section and is represented bya shape that has been given to the side faces of the unit section. Eachsaid unit section has a first side displacement pattern that has been sodefined as to make a signal waveform rise relatively steeply and fallrelatively gently, or a second side displacement pattern that has beenso defined as to make a signal waveform rise relatively gently and fallrelatively steeply. An identification mark is formed at the beginning ofeach said unit section and used to identify the unit section. Theidentification mark has a side displacement pattern, which isdistinguishable from the first and second side displacement patterns,and represents the same information as the subdivided information thatis represented by the shape given to its associated unit section.

In one preferred embodiment of the present invention, the information ispreferably recorded on the optical disk medium on a block basis. Theblock preferably has a predetermined length. The block preferablyincludes a number N of unit sections that are arranged along the trackgroove.

In another preferred embodiment, the side faces of the track groove arepreferably displaced either toward an inner periphery or an outerperiphery of the optical disk medium with respect to a centerline of thetrack groove.

In this particular preferred embodiment, a portion of the side faces,which is shared by at least two of the unit sections, preferably has aconstant displacement period within at least one of the blocks.

In still another preferred embodiment, one-bit subdivided information ispreferably allocated to each said unit section, and a group ofsubdivided information representing N bits is preferably recorded on theN unit sections that are included in each said block.

Specifically, each said N-bit subdivided information group preferablyincludes address information of its associated block to which the N unitsections, where the subdivided information group is recorded, belong.

The present invention further provides another method for readingaddress information from the optical disk medium of the presentinvention. The method includes the steps of: detecting theidentification mark that is provided for each of the unit sections andgenerating a first signal that corresponds to the informationrepresented by the identification mark detected; generating a secondsignal that corresponds to the subdivided information represented by theunit section following the identification mark; and defining thesubdivided information represented by the unit section in accordancewith the first and second signals.

The present invention further provides another apparatus for readingaddress information from the optical disk medium of the presentinvention. The apparatus includes: means for detecting theidentification mark that is provided for each of the unit sections andgenerating a first signal that corresponds to the informationrepresented by the identification mark detected; means for generating asecond signal that corresponds to the subdivided information representedby the unit section following the identification mark; and means fordefining the subdivided information represented by the unit section inaccordance with the first and second signals.

Other features, elements, processes, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of preferred embodiments of the presentinvention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe invention, will be better understood when read in conjunction withthe appended drawings. For the purpose of illustrating the invention,there are shown in the drawings embodiments which are presentlypreferred. It should be understood, however, that the invention is notlimited to the precise arrangements and instrumentalities shown.

FIG. 1A is a plan view of an optical disk medium according to apreferred embodiment of the present invention; and FIG. 1B is a planview illustrating a planar shape of a track groove on the optical diskmedium shown in FIG. 1A;

FIG. 2( a) illustrates plan views showing wobble pattern elements;

FIG. 2( b) illustrates plan views showing four types of wobble patternsformed by combining the elements shown in FIG. 2( a);

FIG. 3A illustrates a basic configuration for an apparatus that canidentify the type of a given wobble pattern by a wobble signal havingamplitude changing with the wobble of a track groove;

FIG. 3B illustrates waveform diagrams showing a wobble pattern of thetrack groove, the wobble signal and a pulse signal;

FIG. 3C illustrates a circuit configuration for extracting the pulsesignal and a clock signal from the wobble signal;

FIG. 4 illustrates a main portion of an optical disk medium according toa first preferred embodiment of the present invention;

FIG. 5 illustrates a configuration for an optical disk reproducingapparatus according to a second preferred embodiment of the presentinvention;

FIG. 6 illustrates a configuration for an optical disk reproducingapparatus according to a third preferred embodiment of the presentinvention;

FIG. 7 illustrates an address reading method according to a fourthpreferred embodiment of the present invention;

FIG. 8 illustrates a configuration for an optical disk reproducingapparatus according to a fifth preferred embodiment of the presentinvention;

FIG. 9 illustrates a detailed configuration for the wobble shapedetector shown in FIG. 8;

FIG. 10 illustrates a main portion of an optical disk medium accordingto a sixth preferred embodiment of the present invention;

FIGS. 11A and 11B illustrate a method for writing a signal on a VFOrecording area 21;

FIG. 12 illustrates a main portion of an optical disk medium accordingto a seventh preferred embodiment of the present invention;

FIG. 13 illustrates a main portion of an optical disk medium accordingto an eighth preferred embodiment of the present invention;

FIGS. 14A and 14B illustrate a signal writing method according to theeighth preferred embodiment;

FIG. 15 illustrates a main portion of an optical disk medium accordingto a ninth preferred embodiment of the present invention;

FIG. 16 illustrates a main portion of an optical disk medium accordingto a tenth preferred embodiment of the present invention;

FIG. 17 illustrates a main portion of an optical disk medium accordingto an eleventh preferred embodiment of the present invention;

FIG. 18 illustrates a main portion of an optical disk medium accordingto a twelfth preferred embodiment of the present invention;

FIG. 19 illustrates a configuration for an apparatus for generating aclock signal and reading an address signal from the optical disk mediumof the twelfth preferred embodiment;

FIG. 20 illustrates main portions of an optical disk medium according toa thirteenth preferred embodiment of the present invention;

FIG. 21 illustrates how an address may be detected in the thirteenthpreferred embodiment;

FIG. 22 illustrates how an address may be detected in the thirteenthpreferred embodiment;

FIG. 23 illustrates a configuration for an apparatus for reading addressinformation from the optical disk medium of the thirteenth preferredembodiment;

FIG. 24 illustrates signal waveform diagrams to describe how theapparatus shown in FIG. 23 may operate; and

FIG. 25 illustrates signal waveform diagrams to describe how theapparatus shown in FIG. 23 may operate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As shown in FIG. 1A, a spiral track groove 2 has been formed on therecording surface 1 of an optical disk medium according to the presentinvention. FIG. 1B illustrates a part of the track groove 2 to a largerscale. In FIG. 1B, a disk center (not shown) exists below the trackgroove 2 and a disk radial direction is indicated by the arrow a. Thearrow b points a direction in which a read/write light beam spot, beingformed on the disk, moves as the disk is rotated. In the followingdescription, a direction parallel to the arrow a will be herein referredto as a “disk radial direction” (or “radial direction” simply), while adirection parallel to the arrow b will be herein referred to as a“tracking direction”.

In a coordinate system in which the light beam spot is supposed to beformed at a fixed location on the disk, a part of the disk irradiatedwith the light beam (which will be herein referred to as a “diskirradiated part”) moves in the direction opposite to the arrow b.

Hereinafter, the X-Y coordinate system illustrated in FIG. 1B will beconsidered. In an optical disk according to the present invention, the Ycoordinate of a location on a side face 2 a or 2 b of the track groovechanges periodically as the X coordinate thereof increases. Such aperiodic location displacement on the groove side face 2 a or 2 b willbe herein referred to as the “wobble” or “wobbling” of the track groove2. A displacement in the direction pointed by the arrow a will be hereinreferred to as an “outward displacement”, while a displacement in thedirection opposite to the arrow a will be herein referred to as an“inward displacement”. Also, in FIG. 1B, one wobble period is identifiedby “T”. The wobble frequency is inversely proportional to one wobbleperiod T and is proportional to the linear velocity of the light beamspot on the disk.

In the illustrated example, the width of the track groove 2 is constantin the tracking direction (as indicated by the arrow b). Accordingly,the amount to which a location on the side face 2 a or 2 b of the trackgroove 2 is displaced in the disk radial direction (as indicated by thearrow a) is equal to the amount to which a corresponding location on thecenterline of the track groove 2 (as indicated by the dashed line) isdisplaced in the disk radial direction. For this reason, thedisplacement of a location on the side face of the track groove in thedisk radial direction will be herein simply referred to as the“displacement of the track groove” or the “wobble of the track groove”.It should be noted, however, that the present invention is not limitedto this particular situation where the centerline and the side faces 2 aand 2 b of the track groove 2 wobble to the same amount in the diskradial direction. Alternatively, the width of the track groove 2 maychange in the tracking direction. Or the centerline of the track groove2 may not wobble but only the side faces of the track groove may wobble.

In the present invention, the wobbling structure of the track groove 2is defined as a combination of multiple types of displacement patterns.That is to say, the planar shape of the track groove 2 does not consistof just the sine waveform shown in FIG. 1B but at least part of it has ashape different from the sine waveform. A basic configuration for such awobbled groove is disclosed in the descriptions of Japanese PatentApplication Nos. 2000-6593, 2000-187259 and 2000-319009 that were filedby the applicant of the present application.

As for the track groove 2 shown in FIG. 1B, the Y coordinate of alocation on the centerline of the groove may be represented by afunction f₀(x) of the X coordinate thereof. In that case, f₀(x) may begiven by “constant·sin(2Πx/T)”, for example.

Hereinafter, the configurations of wobble patterns adopted in thepresent invention will be described in detail with reference to FIGS. 2(a) and 2(b).

FIG. 2( a) illustrates the four types of basic elements that make up awobble pattern of the track groove 2. In FIG. 2( a), smooth sinewaveform portions 100 and 101, a rectangular portion 102 with a steepoutward displacement and a rectangular portion 103 with a steep inwarddisplacement are shown. By combining these elements or portions witheach other, the four types of wobble patterns 104 through 107 shown inFIG. 2( b) are formed.

The wobble pattern 104 is a sine wave with no rectangular portions. Thispattern will be herein referred to as a “basic waveform”. It should benoted that the “sine wave” is not herein limited to a perfect sinecurve, but may broadly refer to any smooth wobble.

The wobble pattern 105 includes portions that are displaced toward thedisk outer periphery more steeply than the sine waveform displacement.Such portions will be herein referred to as “outwardly displacedrectangular portions”.

In an actual optical disk, it is difficult to realize the displacementof a track groove in the disk radial direction vertically to thetracking direction. Accordingly, an edge actually formed is notperfectly rectangular. Thus, in an actual optical disk, an edge of arectangular portion may be displaced relatively steeply compared to asine waveform portion and does not have to be perfectly rectangular. Ascan also be seen from FIG. 2( b), at a sine waveform portion, adisplacement from the innermost periphery toward the outermost peripheryis completed in a half wobble period. As for a rectangular portion, asimilar displacement may be finished in a quarter or less of one wobbleperiod, for example. Then, the difference between these shapes is stilldistinguishable easily enough.

The wobble pattern 106 is characterized by inwardly displaced rectangleswhile the wobble pattern 107 is characterized by both “inwardlydisplaced rectangles” and “outwardly displaced rectangles”.

The wobble pattern 104 consists of the basic waveform alone.Accordingly, the frequency components thereof are defined by a “basicfrequency” that is proportional to the inverse number of the wobbleperiod T. In contrast, the frequency components of the other wobblepatterns 105 through 107 include not only the basic frequency componentsbut also high-frequency components. Those high-frequency components aregenerated by the steep displacements at the rectangular portions of thewobble patterns.

If the coordinate system shown in FIG. 1B is adopted for each of thesewobble patterns 105 through 107 to represent the Y coordinate of alocation on the track centerline by a function of the X coordinatethereof, then the function may be extended into Fourier series. Theexpanded Fourier series will include a term of a sin function having anoscillation period shorter than that of sin(2Πx/T), i.e., a harmoniccomponent. However, each of these wobble patterns includes a fundamentalwave component. The frequency of the basic waveform will be hereinreferred to as a “wobble frequency”. The four types of wobble patternsdescribed above have a common wobble frequency.

In the present invention, instead of modulating the wobble frequency ofthe track groove 2 to write address information thereon, the multipletypes of wobble patterns are combined with each other, thereby recordingvarious types of information, including the address information, on thetrack groove. More specifically, by allocating one of the four types ofwobble patterns 104 through 107 to each predetermined section of thetrack groove, four types of codes (e.g., “B”, “S”, “0” and “1”, where“B” denotes block information, “S” denotes synchronization informationand a combination of zeros and ones represents an address number or anerror detection code thereof) may be recorded.

Next, the fundamentals of an inventive method for reading information,which has been recorded by the wobble of the track groove, from theoptical disk will be described with reference to FIGS. 3A and 3B.

First, FIGS. 3A and 3B will be referred to.

FIG. 3A illustrates a main portion of a reproducing apparatus, whileFIG. 3B illustrates a relationship between the track groove and a readsignal.

The track groove 200 schematically illustrated in FIG. 3B is scanned bya read laser beam 201 so that the spot thereof moves in the directionindicated by the arrow shown in FIG. 3B. The laser beam 201 is reflectedfrom the optical disk to form reflected light 202, which is received atdetectors 203 and 204 of the reproducing apparatus shown in FIG. 3A. Thedetectors 203 and 204 are located apart from each other in a directioncorresponding to the disk radial direction and each output a voltagecorresponding to the intensity of the light received. If the position atwhich the detectors 203 and 204 are irradiated with the reflected light202 (i.e., the position at which the light is received) shifts towardone of the detectors 203 and 204 with respect to the centerline thatseparates the detectors 203 and 204 from each other, then a differenceis created between the outputs of the detectors 203 and 204 (which is“differential push-pull detection”). The outputs of the detectors 203and 204 are input to a differential circuit 205, where a subtraction iscarried out on them. As a result, a signal corresponding to the wobbleshape of the groove 200 (i.e., a wobble signal 206) is obtained. Thewobble signal 206 is input to, and differentiated by, a high-pass filter(HPF) 207. Consequently, the smooth fundamental components that havebeen included in the wobble signal 206 are attenuated and instead apulse signal 208, including pulse components corresponding torectangular portions with steeps gradients, is obtained. As can be seenfrom FIG. 3B, the polarity of each pulse in the pulse signal 208 dependson the direction of its associated steep displacement of the groove 200.Accordingly, the wobble pattern of the groove 200 is identifiable by thepulse signal 208.

Next, referring to FIG. 3C, illustrated is an exemplary circuitconfiguration for generating the pulse signal 208 and a clock signal 209from the wobble signal 206 shown in FIG. 3B.

In the exemplary configuration illustrated in FIG. 3C, the wobble signal206 is input to first and second bandpass filters BPF1 and BPF2, whichgenerate the pulse and clock signals 208 and 209, respectively.

Supposing the wobble frequency of the track is fw (Hz), the firstbandpass filter BPF1 may be a filter having such a characteristic thatthe gain (i.e., transmittance) thereof reaches its peak at a frequencyof 4 fw to 6 fw (e.g., 5 fw). In a filter like this, the gain thereofpreferably increases at a rate of 20 dB/dec, for example, in a rangefrom low frequencies to the peak frequency, and then decreases steeply(e.g., at a rate of 60 dB/dec) in a frequency band exceeding the peakfrequency. In this manner, the first bandpass filter BPF1 canappropriately generate the pulse signal 208, representing therectangularly changing portions of the track wobble, from the wobblesignal 206.

On the other hand, the second bandpass filter BPF2 has such a filteringcharacteristic that the gain thereof is high in a predeterminedfrequency band (e.g., in a band ranging from 0.5 fw to 1.5 fw andincluding the wobble frequency fw at the center) but is small at theother frequencies. The second bandpass filter BPF2 like this cangenerate a sine wave signal, having a frequency corresponding to thewobble frequency of the track, as the clock signal 209.

Hereinafter, preferred embodiments of the optical disk medium accordingto the present invention will be described in detail.

Embodiment 1

A spiral track groove 2 such as that shown in FIG. 1A is also formed onthe recording surface 1 of an optical disk according to this preferredembodiment.

FIG. 4 illustrates the shape of the track groove 2 of this preferredembodiment. The track groove 2 is divided into a plurality of blocks,and a block mark (identification mark) 210 for use as a positioning markis provided between two adjacent blocks. The block mark 210 of thispreferred embodiment is formed by discontinuing the track groove 2 forjust a short length.

The track groove 2 includes a plurality of unit sections 22, 23, andeach block is made up of a predetermined number of unit sections 22, 23.An arbitrary wobble pattern, selected from a plurality of wobblepatterns, may be allocated to each unit section. In the exampleillustrated in FIG. 4, the wobble patterns 106 and 105 shown in FIG. 2(b) are allocated to the unit sections 22 and 23, respectively.

Each of these wobble patterns 105 and 106 carries a one-bit informationelement (i.e., “0” or “1”), which will be herein referred to as“subdivided information”. By identifying the type of the wobble patternallocated to each unit section of the track groove, the contents of thesubdivided information allocated to the unit section can be read.Accordingly, various types of information can be read based on multi-bitsubdivided information.

As described above, the difference in waveform between the wobblepatterns is represented as a difference in gradient between the leadingedges or the trailing edges of the read signals as obtained by thedifferential push-pull detection. Accordingly, the wobble pattern of theunit section 22, for example, is easily identifiable as one of thewobble patterns 105 and 106 shown in FIG. 2( b). However, when thisdetection is performed by differentiating the read signal in theabove-described manner, noise components increase. For that reason, ifthis technique is applied to a high-density optical disk medium thatresults in a low SN ratio, then detection errors may occur. To avoid theoccurrence of such detection errors, the following technique is adoptedin this preferred embodiment.

The information to be written by the user on the disk (which will beherein referred to as “recording information”) is written over severalblocks along the track groove on the recording layer. The recordinginformation is written on a block-by-block basis. Each block extendsfrom the block mark 210 along the track groove 2 and has a predeterminedlength of e.g., 64 kilobytes. A block like this is a unit of informationprocessing and may mean an ECC block, for example. Each block is made upof a number N (which is a natural number) of sub-blocks. When each blockhas a length of 64 kilobytes and each sub-block has a length of 2kilobytes, the number N of sub-blocks included in one block is 32.

In this preferred embodiment, the areas on the track groove where theinformation for respective sub-blocks should be written correspond tothe unit sections 22, 23 of the track groove.

Since one-bit subdivided information “0” or “1” is recorded on each ofthe unit sections 22 and 23, a group of subdivided information of N=32bits is allocated to each block. In this preferred embodiment, theaddress of the block is indicated by this group of subdividedinformation of 32 bits.

For example, where each unit section has a length of 2,418 bytes (=2,048bytes plus parity) and one wobble period has a length corresponding to11.625 bytes, a wobble pattern for 208 periods is included in each unitsection. Accordingly, the wobble signal 206 shown in FIGS. 3B and 3C maybe detected over 208 wobble periods (i.e., a wave number of 208) toidentify the type of the given wobble pattern. For that reason, even ifsome detection errors have been caused by noise during signal reading,the subdivided information is identifiable accurately enough.

More specifically, the differentiated waveform of the differentialpush-pull signal (i.e., the pulse signal 208) may be sampled and heldevery time the signal rises or falls. And if the accumulated value ofthe number of rises is compared to that of the number of falls, then thenoise components are canceled. As a result, the subdivided informationcomponents can be extracted highly accurately.

The block mark 210 shown in FIG. 4 is formed by discontinuing the trackgroove 2 for just a short length. Accordingly, if information isoverwritten on that part of the recording layer over the block mark 210,then some problems will occur. Specifically, since the quantity of lightreflected greatly changes depending on whether or not the groove ispresent at the spot, the existence of the block mark 210 causes adisturbance in the read signal. Thus, in this preferred embodiment, aVFO (variable frequency oscillator) recording area 21 is allocated to anarea 21 of a predetermined length including the block mark 210. The VFOrecording area 21 is an area where a monotone signal VFO is written. VFOis a signal for locking a PLL required for reading the recordedinformation. Even when there is any disturbance or variation, the VFOsignal would cause a jitter just locally but no errors. Also, the VFOsignal has a single repetitive frequency. Accordingly, it is possible toseparate the disturbance caused by the block mark. However, the signalto be written on the VFO recording area 21 does not have to have asingle frequency, but may have a particular pattern and a spectralbandwidth narrow enough to separate the frequency thereof from that of asignal corresponding to the block mark 210.

Embodiment 2

Hereinafter, an optical disk reproducing apparatus having the functionof reading an address on the optical disk medium of the first preferredembodiment will be described with reference to FIG. 5.

A laser beam, emitted from the optical head 331 of this reproducingapparatus, impinges onto an optical disk 1, thereby forming a light spoton the track groove of the optical disk 1. A drive mechanism iscontrolled in such a manner that the light spot moves on the trackgroove as the optical disk 1 is rotated.

The optical head 331 then receives the laser beam that has beenreflected by the optical disk 1, thereby generating an electric signal.The electric signal is output from the optical head 331 and then inputto a read signal processor 332 where the electric signal is subjected tooperation processing. In response to the signal supplied from theoptical head 331, the read signal processor 332 generates and outputs afully added signal and a wobble signal (i.e., push-pull signal).

The wobble signal is input to a wobble PLL circuit 333. The wobble PLLcircuit 333 generates a clock signal from the wobble signal and thendelivers the clock signal to a timing generator 335. The clock signalhas a frequency obtained by multiplying the wobble frequency. It shouldbe noted that before the wobble PLL circuit 333 is phase-locked, atiming signal may also be generated by using a reference clock signalalthough the precision is inferior.

The fully added signal, output from the read signal processor 332, isinput to a block mark detector 334. In accordance with the fully addedsignal, the block mark detector 334 locates the block mark 210. In theoptical disk of the first preferred embodiment, the laser beam,reflected from a part where the block mark 210 is present, has a higherintensity than the other parts. Accordingly, when the level of the fullyadded signal exceeds a predetermined level, the block mark detector 334generates a block mark detection signal and sends it out to the timinggenerator 335.

In response to the block mark detection signal and the clock signal, thetiming generator 335 counts the number of clock pulses from thebeginning of a block. By performing this counting, it is possible todetermine the timing at which the wobble signal should rise or fall, thetiming at which the information is subdivided and the timing at whicheach block is sectioned.

A first shape counter 336 counts the number of times the gradient of thewobble signal rising is equal to or greater than a predetermined valueU_(TH) for each unit section. More specifically, if the gradient of thepush-pull signal is equal to or greater than the predetermined valueU_(TH) when the wobble signal rises, the counter 336 increments itscount C1 by one. On the other hand, if the gradient is less than U_(TH),then the counter 336 does not change its count C1 but holds it. Thetiming at which the wobble signal rises is defined by the output signalof the timing generator 335.

A second shape counter 337 counts the number of times the gradient ofthe wobble signal falling is equal to or smaller than a predeterminedvalue D_(TH) for each unit section. More specifically, if the gradientof the push-pull signal is equal to or smaller than the predeterminedvalue D_(TH) when the wobble signal falls, the counter 337 incrementsits count C2 by one. On the other hand, if the gradient is larger thanD_(TH), then the counter 337 does not change its count C2 but holds it.The timing at which the wobble signal falls is also defined by theoutput signal of the timing generator 335.

A subdivided information detector 338 compares the count C1 of the firstshape counter 336 with the count C2 of the second shape counter 337 inresponse to the timing signal that has been generated by the timinggenerator 335 to indicate the timing at which the information should besubdivided. If C1≧C2 is satisfied for a certain unit section, then thedetector 338 outputs “1” as the subdivided information of the unitsection. On the other hand, if C1<C2 is satisfied for a unit section,then the detector 338 outputs “0” as the subdivided information of theunit section. In other words, the detector 338 decides the type of thewobble signal by majority on a unit section basis.

An error corrector 339 makes an error correction on the group ofsubdivided information allocated to a plurality of unit sectionsincluded in one block, thereby obtaining address information.

These circuits do not have to be separately implemented as mutuallyindependent circuits. Alternatively, a single circuit component may beshared by a plurality of circuits. Also, the functions of these circuitsmay be executed by a digital signal processor whose operation iscontrolled in accordance with a program pre-stored on a memory. The samestatement will also be true of each of the following various preferredembodiments of the present invention.

Embodiment 3

Another preferred embodiment of the optical disk reproducing apparatusaccording to the present invention will be described with reference toFIG. 6. The optical disk reproducing apparatus of this preferredembodiment is different from the apparatus for reading addressinformation according to the second preferred embodiment in that thereproducing apparatus further includes an erasure detector 340. Theerror corrector 339 also has a different function. In the otherrespects, the apparatus of this preferred embodiment is the same as thecounterpart of the second preferred embodiment. Thus, the description ofthe components commonly used for these two preferred embodiments will beomitted herein.

The erasure detector 340 compares the count C1 output from the firstshape counter 336 with the count C2 output from the second shape counter337 for each unit section. And when an inequality -E<C1-C2<+E issatisfied with respect to a predetermined value E, the detector 340outputs an erasure flag of “1” indicating that the subdividedinformation is not definitely identifiable. On the other hand, if theinequality -E<C1-C2<+E is not satisfied, the detector 340 outputs anerasure flag of “0”.

If the erasure flag is “1”, the error corrector 339 erases thesubdivided information, thereby making an error correction compulsorily.

In this preferred embodiment, error bits are erased using the erasureflags in this manner. Thus, the number of error-correctible bits of anerror correction code is doubled.

It should be noted that as the erasure flag, “0” may be output whenC1-C2≦-E, “X” may be output when -E<C1-C2<+E and “1” may be output when+E≦C1-C2. In that case, if the erasure flag is “X”, the error correctionmay be made compulsorily.

As described above, in the optical disk reproducing apparatus of thispreferred embodiment, if subdivided information is not definitelyidentifiable due to a small difference between the first and secondshape counts, then bits in question are erased during an errorcorrection process. In this manner, the error correction ability isimproved and an address can be read more reliably.

Embodiment 4

An inventive method for reading an address on an optical disk mediumwill be described with reference to FIG. 7.

A wobble shape 351 is schematically illustrated on the upper part ofFIG. 7. In the left half of the wobble shape 351, falling displacementsare steep. In the right half thereof on the other hand, risingdisplacements are steep.

The wobble signal 352 as represented by a push-pull signal has had itsquality deteriorated by noise or waveform distortion.

A digitized signal 353 is obtained by slicing the wobble signal 352 atzero level. A differentiated signal 354 is obtained by differentiatingthe wobble signal 352. The differentiated signal 354 containsinformation about the gradients of the wobble shape. A number of peaks,reflecting noise or waveform distortion, are observed here and there inaddition to those peaks representing the gradients detected fordisplacement points.

For the sake of simplicity, only first and second parts 355 and 356 thatare arbitrarily selected from the wobble signal will be described.

In the first part 355 of the wobble signal, when the values 357 and 358of the differentiated signal 354 that are sampled with respect toleading and trailing edges of the digitized signal 353, respectively,have their absolute values compared with each other, the sampled value358 has the greater absolute value. Accordingly, it may be decided thatthe wobble signal including the first part 355 has a wobble pattern inwhich a falling displacement is steeper than a rising displacement.

In the same way, as for the second part 356 of the wobble signal, whenthe values 359 and 360 of the differentiated signal 354 that are sampledwith respect to leading and trailing edges of the digitized signal 353,respectively, have their absolute values compared with each other, thesampled value 359 has the greater absolute value. Accordingly, it may bedecided that the wobble signal including the second part 356 has awobble pattern in which a rising displacement is steeper than a fallingdisplacement.

By making such a decision on a wobble period basis and by accumulatingthe decisions, the type of each subdivided information unit isidentifiable by majority.

In this manner, according to the address reading method of the presentinvention, the differentiated signal is sampled only at the timingscorresponding to the edges of the signal obtained by digitizing thewobble signal, and the sampled values are compared with each other. As aresult, the gradients of the wobble shape at the displacement points aredetectable highly reliably even under some disturbance such as noise orwaveform distortion.

Embodiment 5

Another optical disk reproducing apparatus for reading an address on anoptical disk according to the present invention will be described withreference to FIG. 8.

The reproducing apparatus of this preferred embodiment is different fromthe counter-part shown in FIG. 5 in that the apparatus of this preferredembodiment includes a wobble shape detector 361. The wobble shapedetector 361 identifies a given wobble shape as a first shape with asteep rising displacement or as a second shape with a steep fallingdisplacement on a wobble period basis, thereby outputting wobble shapeinformation to the subdivided information detector 338. In accordancewith the wobble shape information obtained from the wobble shapedetector 361, the subdivided information detector 338 determines whichshape has been detected the greater number of times, the first shape orthe second shape. Then, the detector 338 identifies and outputs thesub-divided information allocated to a given subdivided informationunit.

The subdivided information detector 338 may include: a counter forobtaining the number of times that a signal indicating the detection ofthe first shape has been received in accordance with the wobble shapeinformation received; and another counter for obtaining the number oftimes that a signal indicating the detection of the second shape hasbeen received in accordance with that information. By comparing thecounts of these two shapes with each other, a decision by majority maybe made. Alternatively, an up/down counter may also be used to incrementthe count by one when the first shape is detected and to decrement thecount by one when the second shape is detected. In that case, thesubdivided information may be represented by the sign of the count ofthe up/down counter, i.e., seeing whether the count of the up/downcounter is positive or negative, at the end of a given unit section.

Next, it will be described in detail with reference to FIG. 9 how thewobble shape detector 361 operates.

The wobble shape detector 361 includes a bandpass filter (BPF) 362,which receives the push-pull signal (i.e., the wobble signal) andreduces unwanted noise components thereof. This BPF 362 may pass thefundamental (basic) frequency components of the wobble signal andharmonic frequency components including wobble gradient information.Supposing the wobble signal has a basic frequency of fw, a bandpassfilter having a band ranging from ½ fw to 5 fw is preferably used toallow a good margin for possible variation in linear velocity.

The output of the BPF 362 is input to a gradient detector 363 and adigitizer 365.

The gradient detector 363 detects the gradient of the wobble signal.This “gradient” detection may be carried out by differentiating thewobble signal. Instead of the differentiator, a high-pass filter (HPF)for extracting only harmonic components including gradient informationmay also be used. The output of the gradient detector 363 is deliveredto a rise value acquirer 366 and an inverter 364.

The inverter 364 inverts the output of the gradient detector 363 withrespect to the zero level and then outputs the inverted value to a fallvalue acquirer 367.

The digitizer 365 detects rising and falling zero-cross timings of thewobble signal.

The “rising zero-cross timing” herein means a time at which the wobblesignal changes from “L” level into “H” level. On the other hand, the“falling zero-cross timing” herein means a time at which the wobblesignal changes from “H” level into “L” level.

The rise value acquirer 366 samples and holds the gradient of the wobblesignal, i.e., the output of the gradient detector 363, at the risingzero-cross timing that has been detected by the digitizer 365. In thesame way, the fall value acquirer 367 samples and holds the invertedgradient of the wobble signal, i.e., the output of the inverter 364, atthe falling zero-cross timing that has been detected by the digitizer365.

In this case, the value sampled by the rise value acquirer 366 is apositive value because this value represents the gradient of a risingedge. The value sampled by the fall value acquirer 367 is also apositive value because this value represents the inverted gradient of afalling edge. That is to say, the values sampled by the rise and fallvalue acquirers 366 and 367 correspond to the absolute values of therespective gradients.

A comparator 369 compares the absolute value of the rising edge gradientas sampled and held by the rise value acquirer 366 to the absolute valueof the falling edge gradient as sampled and held by the fall valueacquirer 367 after a predetermined time has passed since the fallingzero-cross timing of the wobble signal. This predetermined amount oftime delay is caused by a delay circuit 368. If the value of the risevalue acquirer 366 is found the greater, the comparator 369 outputswobble shape information indicating the first shape. Otherwise, thecomparator 369 outputs wobble shape information indicating the secondshape. That is to say, by comparing only the gradients at the rising andfalling zero-cross timings, at which the wobble signal gradientinformation is most reliable (i.e., the differentiated values thereofwill be the maximum and minimum, respectively), to each other, thewobble shape is detectable accurately enough.

In this preferred embodiment, the same signal is input to both thedigitizer 365 and the gradient detector 363. However, the presentinvention is not limited to this particular preferred embodiment. Todetect the zero-cross timings of the wobble signal even more accurately,the output of the BPF 362 may be input to the digitizer 365 by way of alow-pass filter (LPF). Also, the BPF 362 may be replaced with two typesof BPFs with mutually different characteristics that are provided forthe gradient detector 363 and the digitizer 365, respectively. In thatcase, to match the phases of the wobble signal that has been passedthrough these BPFs, a delay corrector is preferably further providedseparately.

As described above, in the optical disk reproducing apparatus of thispreferred embodiment, the gradients of a wobble signal includingsubdivided information are sampled and held at zero-cross timings of thewobble signal and then the values held are compared to each other. Inthis manner, the wobble shape is identifiable accurately enough anddetection errors of subdivided information as caused by noise, forexample, are reducible.

Embodiment 6

FIG. 10 illustrates a configuration in which a block mark 210 is locatedapproximately at the center of a VFO recording area 21. In the exampleillustrated in FIG. 10, a wobble having a rectangular waveform has beenformed in the VFO recording area 21. However, the present invention isnot limited to this particular preferred embodiment.

Hereinafter, it will be described with reference to FIGS. 11A and 11Bhow to write a signal on the VFO recording area 21. In FIGS. 11A and11B, the wobble formed on the track groove 2 is omitted for the sake ofsimplicity.

FIG. 11A illustrates a situation where a signal corresponding to oneblock is written on the track groove 2. A recording signal for one blockincludes data (DATA) 202 and VFOs 201 and 203.

Writing on each block begins with the VFO 201. In this preferredembodiment, the VFO 201 is written within the VFO recording area 21 andthe writing start point of the VFO 201 is ahead of the block mark 210.After the VFO 201 has been written, the DATA 202 for one block iswritten and then the VFO 203 is written finally. The VFO 203 is writtenwithin the VFO recording area 31 and the writing end point of the VFO203 is behind the block mark 310. That is to say, in this preferredembodiment, information starts to be recorded before the block mark,located at the beginning of an intended recording area, is reached, andthen finishes being recorded after the block mark, located at the end ofthe intended recording area, has been passed.

If data starts to be written at the center of the block mark 210, thenthe recording film deteriorates considerably at its part where the blockmark 210 is present. The block mark 210 of this preferred embodiment isformed by discontinuing the track groove 2 for just a short length.Accordingly, steps have been formed on the track groove where the blockmark 210 is present. In recording information on those stepped parts,the information needs to be recorded on the recording film byirradiating those parts of the recording film with a high-energy laserbeam so that the irradiated parts will be given a high thermal energy.In this case, steep temperature gradients are formed before and afterthose parts irradiated with the laser beam. These temperature gradientsproduce a stress in the recording film. If any of the steps exists inthe stressed part, then a small crack might be formed in the recordingfilm. Once that small crack has been formed in the recording film, thecrack will expand every time the write operation is repeatedly carriedout. Then, the film might be broken in the end.

In this preferred embodiment, to prevent such film breakage, the writingstart and end points are defined in the areas where no block marks 210or 301 are present.

The VFO is a dummy signal for preparing for data reading. While the VFOsignal is being read, the slice level of the data is feedback-controlledat the center of the read signal and the PLL is locked to extract aclock signal. To read data with high fidelity, the read data signalneeds to be digitized and clocked accurately enough. If a VFO signalinterval is too short, then the data starts to be read before the PLLhas been locked sufficiently, thus possibly causing errors in the datathat has been read out from the beginning of a block. Accordingly, theVFO preferably starts to be written ahead of the block mark and ispreferably provided with a sufficiently long area.

It should be noted that if data has already been written on the previousblock, then a VFO for the current block to be written might beoverwritten on a VFO for the previous block as shown in FIG. 11B. Inthat case, part of the VFO signal already written is erased. Also, thepreexistent VFO may not be in phase with the overwritten VFO.Accordingly, it is not preferable to get the PLL locked for the currentblock by using the VFO of the previous block.

The foregoing description of this preferred embodiment relates to theVFO writing start point. Similar recording film deterioration is alsoobserved around the data writing end point. However, the writing endpoint is preferably behind the block mark 310, not before. If thewriting end point was located ahead of the block mark 310, then a gapmight be formed between the current block and the following block. Thisgap is an area that is not irradiated with the high-power light and inwhich no marks are formed. Just like the steps, such a gap mightcontribute to the film deterioration. Accordingly, the VFO at the end ofthe previously written block preferably overlaps with the VFO at thebeginning of the current block to be written. This VFO overlap isachieved by setting the VFO writing start point ahead of the block mark210 and the VFO writing end point behind the block mark 310,respectively, as shown in FIG. 11A.

The distance between the block mark and the VFO writing start or endpoint is preferably about 10 times or more as long as the beam spot sizeof the laser light for writing. A beam spot size is obtained by dividingthe wavelength of laser light by an NA value. Accordingly, when anoptical head, which emits laser light having a wavelength of 650 nm andhas an NA of 0.65, is used, the size of a beam spot formed on a disk is1 μm (=wavelength/NA). In that case, the writing start or end point ispreferably 10 μm or more distant from the block mark. However, thatreference distance obtained by multiplying the beam spot size by ten maybe correctible depending on the properties (e.g., thermal conductivity,in particular) of the recording film.

It should be noted, however, that when the write operation is startedahead of the block mark 210, the block mark 210 has not been detectedyet. Accordingly, to start writing before the block mark just asintended, the location of the block mark should be predicted orestimated in some way or other. For example, after the block mark of theprevious block has been detected, the number of clock pulses of theclock signal may be counted. And when the count reaches a predeterminednumber, the VFO may start to be written for the next block.

Embodiment 7

An optical disk medium according to a seventh preferred embodiment ofthe present invention will be described with reference to FIG. 12. Inthe sixth preferred embodiment described above, the block mark 210 islocated approximately at the center of the VFO recording area 21. On theother hand, according to this preferred embodiment, a block mark 211 islocated closer to the previous block with respect to the center of theVFO recording area 21 as shown in FIG. 12. In such a configuration, theVFO may be longer at the beginning.

Embodiment 8

An optical disk medium according to an eighth preferred embodiment ofthe present invention will be described with reference to FIGS. 13, 14Aand 14B. The block mark 210 of this preferred embodiment is made up oftwo sub-marks 210 a and 210 b. According to this configuration, thewrite operation can be timed more easily. That is to say, since twomarks have been formed, the write operation may be started after themark 210 b at the beginning of a block has been detected and before themark 210 a is detected. Also, the write operation may be ended after thesecond mark 210 a, located at the beginning of the next block, has beendetected.

In this manner, the writing start point can be defined accurately enoughwithout counting the number of clock pulses after the block mark of theprevious block has been detected.

It should be noted that to avoid the film deterioration, the spacebetween these marks 210 a and 210 b is preferably sufficiently wide.Specifically, to make the distance between the writing start point andthe mark 210 a or 210 b about 10 times or more as long as the beam spotsize, the space between the marks 210 a and 210 b is preferably about 20times or more as long as the beam spot size. For example, where the sizeof a beam spot formed on an optical disk is 1 μm, this space ispreferably 20 μm or more.

Embodiment 9

An optical disk according to a ninth preferred embodiment of the presentinvention will be described with reference to FIG. 15. In each of thesixth, seventh and eighth preferred embodiments described above, theblock mark 210 is formed by discontinuing the track groove 2 for just ashort length. In such a part where the track groove is discontinued, nogroove exists. Accordingly, that part is flat and is called a “mirrormark”. A mirror mark reflects read light at a high reflectance and iseasily detectable. In this preferred embodiment, however, the block markis not formed as a mirror mark but a block mark 218 in a different shapeis adopted. Hereinafter, this block mark 218 will be described indetail.

In this preferred embodiment, the wobble phase of the track groove ispartially inverted inside the VFO recording area 21 and this part withthe inverted phase is used as the block mark 218 as shown in FIG. 15.

As described above, the block mark 210 as a mirror mark advantageouslyensures high positioning accuracy and is easily detectable. However, ifthe SN ratio is low, then detection errors increase considerably. Incontrast, if the track groove is formed in such a manner that the wobblephase before the block mark 218 is the inverse of the wobble phase afterthe block mark 218, the passage of the block mark 218 may be sensed atany time by observing the wobble phase after the block mark 218 has beenpassed. This passage is sensible even if the wobble phase change point(i.e., the block mark 218) itself could not be located due to noise, forexample.

Embodiment 10

Another preferred embodiment of the inventive optical disk will bedescribed with reference to FIG. 16. In this preferred embodiment, twoblock marks 218 a and 218 b are provided inside each VFO recording area21. Each of these block marks 218 a and 218 b is formed by inverting thewobble phase of the track groove.

The main difference between this preferred embodiment and the preferredembodiment illustrated in FIG. 15 is whether the wobble phase isinverted between a pair of blocks an odd number of times or an evennumber of times. As shown in FIG. 15, where the wobble phase is invertedjust once (i.e., an odd number of times) within each VFO recording area21, the wobble phase will be kept inverted to that of the previous blocksince the phase has been inverted and until the next block mark ispassed. As a result, if a clock signal is extracted as it is from thewobble of the track groove by a PLL synchronization technique, then theoutput of the phase comparator of the PLL will have its polarityinverted and the PLL will slip disadvantageously. For that reason, ifthe wobble phase is inverted an odd number of times as in the exampleillustrated in FIG. 15, the polarity of the PLL needs to be invertedafter the block mark has been passed.

In contrast, according to this preferred embodiment, the phase that hasbeen once inverted (at the block mark 218 a) is inverted again (at theblock mark 218 b). Thus, the wobble phase becomes the same as that ofthe previous block. Accordingly, there is no need to invert the polarityof the PLL.

In each VFO recording area 21, the interval between the block marks 218a and 218 b needs to be longer than expected defect noise. However, ifthis interval is longer than the response time of the PLL, theprobability of occurrence of the slip increases. In view of theseconsiderations, the interval between the block marks 218 a and 218 bwithin each VFO recording area 21 is preferably about three to about tentimes as long as the wobble frequency.

It should be noted that the number of the block marks 218 a, 218 binside each VFO recording area 21 is not limited to two but may beanother even number to achieve effects similar to those of thispreferred embodiment. However, more than four block marks 218 a, 218 bshould not be formed within a limited length in view of the density ofintegration.

In the ninth and tenth preferred embodiments described above, the blockmarks are formed by inverting the wobble phase. However, as long as thephase difference is detectable, the phases before and after the blockmark do not have to be shifted from each other by 90 degrees precise.The shift in wobble phase at the block mark is preferably from 45degrees to 135 degrees, for example.

Embodiment 11

Next, an eleventh preferred embodiment of the present invention will bedescribed with reference to FIG. 17.

This preferred embodiment is different from the sixth through tenthpreferred embodiments described above in the configuration of the blockmark 219. Specifically, the block mark 219 of this preferred embodimentis defined by a wobble having a frequency different from the wobblefrequency of the groove located inside the block. In the exampleillustrated in FIG. 17, the wobble frequency of the block mark 219 ishigher than that inside the block. Accordingly, if part of a readsignal, which has a locally different wobble frequency, is separated oridentified by processing the read signal using a band pass filter, forexample, then the block mark 219 can be located highly accurately.

In the optical disk medium of this preferred embodiment, the block mark219 is also formed inside the VFO recording area 21, and VFO data isalso written on the area where the block mark 219 is present.

The wobble frequency of the block mark 219 is preferably defined 1.2 to3.0 times as high as, more preferably 1.5 to 2.0 times as high as, thewobble frequency inside the block. The reason is as follows.Specifically, if the wobble frequency of the block mark 219 is too closeto that inside the block, then it is hard to detect the block mark 219.On the other hand, if the wobble frequency of the block mark 219 is toomuch higher than that inside the block, then the former wobble frequencywill get closer to the signal frequency of the information to be writtenon the recording film. As a result, these signals will interfere witheach other disadvantageously.

It should be noted that in the space between a pair of blocks, a wobblehaving the same frequency as the wobble frequency inside the blocks ispreferably formed except the area of the block mark 219. In theblock-to-block space, however, the wobble shape is preferably differentfrom the wobble shape inside the blocks. In the example illustrated inFIG. 17, the block-to-block groove wobbles in a sine wave curve.

Embodiment 12

Next, a twelfth preferred embodiment of the present invention will bedescribed with reference to FIG. 18.

In this preferred embodiment, no shape that has its amplitude, frequencyor phase changed locally is used as the block mark, but a groove itselfwobbling in a sine wave curve is used as the block mark. Also, thebeginning of each sub-block 221 or 222 includes a wobble 228 or 229 witha locally changed frequency.

By defining such an area having a wobble frequency different from thefundamental wobble frequency at the beginning of each sub-block in thismanner, the boundary between the sub-blocks is detectable correctly. Inthe preferred embodiments described above, a sub-block is located bycounting the number of wobbles from the block mark. On the other hand,in this preferred embodiment, a sub-block can be located by detectingthe sub-block marks 228, 229 provided for the respective sub-blocks.

It should be noted that a block mark similar to the counterpart of anyof the preferred embodiments described above may be formed at anappropriate position inside the VFO recording area 21. Also, in thispreferred embodiment, the sub-block mark 228, 229 having a locallydifferent wobble frequency is formed at the beginning of each sub-block221, 222. Alternatively, the sub-block mark 228, 229 may be located atthe end of each sub-block. Also, the sub-block marks 228, 229 do nothave to be provided for all sub-blocks but may be provided for onlyodd-numbered or even-numbered sub-blocks.

Because of the same reasons as those described above, the wobblefrequency of the sub-block marks 228, 229 is preferably defined 1.2 to3.0 times as high as, more preferably 1.5 to 2.0 times as high as, thatof the other parts.

The sub-block marks 228, 229 are preferably used to indicate thebeginning of their sub-blocks but may represent any other type ofinformation. For example, multiple sub-block marks included in a blockmay represent either the address of the block or that of any otherassociated block. Or any other type of information may be recorded byusing the sub-block marks. When the address of a block is recorded byusing a plurality of sub-block marks, the same address information asthat formed by the shape of wobbles is recorded additionally in the sameblock. Thus, the address can be read much more reliably.

In recording multi-bit information as a combination of these sub-blockmarks, the sub-block marks should have mutually different andidentifiable shapes corresponding to two or more values. For thispurpose, the wobbles of those sub-block marks may be given mutuallydifferent frequencies or may be subjected to mutually different types ofphase modulation.

Next, a circuit configuration for generating a clock signal and readingaddress information from an optical disk medium according to a preferredembodiment of the present invention will be described with reference toFIG. 19.

First, a photodetector 371 that has been divided in a direction verticalto the tracking direction (i.e., in the disk radial direction) and adifferential amplifier 372 are used to generate an electric signalincluding signal components corresponding to the wobble of the groove.Next, a low-pass filter (LPF) 374 extracts only the fundamental periodcomponents of a wobble signal from this read signal. The signalconsisting of the fundamental period components is supplied to a clockgenerator 373. The clock generator 373 may be implemented as a PLLcircuit, for example, and multiplies the fundamental period signalreceived by a predetermined number, thereby generating a clock signalfor use in read/write signal synchronization processing.

On the other hand, a high-pass filter (HPF) 375 selectively passes theharmonic components included in the read wobble signal. The output ofthe high-pass filter 375 includes: high frequency componentscorresponding to the sub-block marks 228 and 229 shown in FIG. 18; andsteep edge components of a saw-tooth like signal representing asaw-tooth like wobble.

A sub-block mark detector 377 detects the wobble components having apredetermined frequency and corresponding to the sub-block marks 228 and229. On detecting these marks 228 and 229, the detector 377 generates atiming signal. The timing signal is output from the sub-block markdetector 377 to an address decoder 378. As described above, a steep edgeof a saw-tooth like wobble has its polarity inverted depending onwhether it represents “1” or “0” of address information. In accordancewith the output of the high-pass filter 375, an address informationdetector 376 detects this polarity inversion and sends out a bit streamto the address decoder 378. On receiving this bit stream, the addressdecoder 378 decodes the address information in response to the timingsignal that has been output from the sub-block mark detector 377.

In the preferred embodiments described above, an identification mark, onwhich signals can be overwritten, is formed for each block and anaddress is represented by the wobble of the groove. As a result, anoptical disk medium, on which information can be stored on ablock-by-block basis and which is suitably applicable to high-densityrecording, is provided. Also, by starting or ending a write operation ata position sufficiently distant from this identification mark, thedeterioration of the recording film is reducible.

Embodiment 13

Hereinafter, a thirteenth preferred embodiment of the present inventionwill be described with reference to FIGS. 20 through 25.

In this preferred embodiment, a sub-block mark 238 a or 239 a, includingphase information, is provided for a portion of each sub-block 221 or222 as shown in FIG. 20. As already described for the twelfth preferredembodiment, the sub-block mark 238 a or 239 a does not have to beprovided just for the purpose of indicating the beginning of itsassociated sub-block 221 or 222. For example, to increase thereliability of address information to be read out from the sub-block 221or 222, the same address information may be represented not only by thewobble 238 b or 239 b but also by the sub-block mark 238 a or 239 awithin the same sub-block 221 or 222.

In this preferred embodiment, the sub-block mark 238 a that has beenformed in the sub-block 221 has a wobbled shape having a non-invertedphase. This shape corresponds to address information “1” as the wobble238 b of the same sub-block 221 does. On the other hand, the sub-blockmark 239 a that has been formed in the sub-block 222 has a wobbled shapehaving an inverted phase. This shape corresponds to address information“0” as the wobble 239 b of the same sub-block 222 does.

By sensing whether each of these sub-block marks 238 a and 239 a is inphase or out of phase with a PLL clock signal, supplementary addressinformation can be obtained.

The phase of the sub-block mark 238 a or 239 a may be detected by acircuit such as that shown in FIG. 23 that utilizes a heterodynedetection technique.

Hereinafter, a phase detection method according to the thirteenthpreferred embodiment of the present invention will be described withreference to FIGS. 21 through 25.

Suppose a read signal S is the output signal of the differentialamplifier 372 shown in FIG. 19, for example. As shown in FIG. 23, theread signal S is input to BPF1 501, BPF2 511 and multiplier 504. The BPF1 501 extracts a wobble basic frequency signal from the read signal Sand then outputs it to a PLL 502. In response, the PLL 502 generates acarrier signal (i.e., first sync signal) C1 and outputs it to themultiplier 504. The carrier signal C1 is synchronized with the wobblebasic frequency signal and has a frequency equal to the wobble basicfrequency.

When this carrier signal C1 and the read signal S are multipliedtogether by the multiplier 504, a multiplied signal can be obtained. Asshown in FIGS. 21 and 22, the polarity of the multiplied signal may beeither positive or negative depending on whether the supplementaryaddress information represented by the sub-block mark 238 a or 239 a is“1” or “0”.

FIG. 21 is a timing chart showing a situation where the supplementaryaddress information represented by the sub-block mark 238 a is “1”,while FIG. 22 is a timing chart showing a situation where thesupplementary address information represented by the sub-block mark 239a is “0”. In FIGS. 21 and 22, the multiplied signal is identified byS×C1.

Next, it will be described in further detail with reference to FIG. 24how the multiplied signal S×C1 is generated. Two types of read signals Shaving mutually inverse phases are shown in portion (a) of FIG. 24. Afirst read signal S is indicated by the solid curve, while a second readsignal S, of which the phase is shifted from that of the first readsignal S by 180 degrees, is indicated by the dashed curve.

As can be seen from portions (a) and (b) of FIG. 24, the carrier signalC1 has been generated so as to be synchronized with, and have the samefrequency as, the read signals S. As shown in portion (b) of FIG. 24,the carrier signal C1 has a waveform that alternates between a zerovoltage level “0” and a positive voltage level “1”. Accordingly, theproduct S×C1 of the first read signal S indicated by the solid curve inportion (a) of FIG. 24 and the carrier signal C1 shown in portion (b) ofFIG. 24 has a waveform indicated by the solid curve shown in portion (c)of FIG. 24. On the other hand, the product S×C1 of the second readsignal S indicated by the dashed curve in portion (a) of FIG. 24 and thecarrier signal C1 shown in portion (b) of FIG. 24 has a waveformindicated by the dashed curve shown in portion (c) of FIG. 24. In thismanner, the multiplied signal S×C1 has its polarity determined by one ofthe two types of phases of the first and second read signals S.

When this multiplied signal S×C1 is integrated for a predeterminedperiod of time by the integrator 505 shown in FIG. 23, the products S×C1will be accumulated in the positive or negative domain to produce theintegrated signal ACC shown in FIG. 21 or 22. The “predetermined period”corresponds to an interval in which that portion of the sub-blockincluding the sub-block mark 238 a or 239 a is scanned by the read laserbeam. In this interval, a gate signal G1 is generated to enable theprocessing performed by the integrator 505 as shown in FIG. 21. In otherwords, the integration operation is started on the leading edge of thegate signal G1 and ended on the trailing edge of the gate signal G1.

The gate signal G1 may be generated in the following manner.Specifically, the number of wobbles may be counted one by one from oneof the block marks 218 a and 218 b shown in FIG. 16, for example. Andthe gate signal G1 may be generated at a time when the beam spot isexpected to pass the sub-block mark. It should be noted that any othertype of block mark may be used instead of the block marks 218 a and 218b shown in FIG. 16.

The information represented by the wobble 238 b or 239 b may also bedetected by a similar method. Suppose the BPF2 511 shown in FIG. 23 is afilter with a transmission band having a center frequency that is twiceas high as the wobble basic frequency of the read signals S. In thatcase, the BPF2 511 extracts a second harmonic signal S2, constitutingthe sawtooth wave, from the read signal S corresponding to the sawtoothwobble 238 b or 239 b as shown in FIGS. 21 and 22. In addition, thephase polarity of the second harmonic signal S2 detected invertsdepending whether the address information represented by the sawtoothwobble 238 b or 239 b is “1” or “0”, i.e., whether the wobble 238 b or239 b is characterized by steep rising displacements or steep fallingdisplacements. Hereinafter, this point will be described in furtherdetail with reference to FIG. 25.

When the wobble pattern of the wobble 238 b or 239 b is extended toFourier series, it can be seen that the wobble pattern is represented bya superposition of a waveform component oscillating in a fundamentalperiod and a plurality of waveform components oscillating in a halfperiod. Accordingly, the read signal S, having a waveform correspondingto the wobble pattern of the wobble 238 b or 239 b, is approximatelyrepresented by a superposition of the basic waveform having the basicfrequency shown in portion (a) of FIG. 25 and the second harmonic S2having a frequency twice as high as the basic frequency as shown inportion (b) of FIG. 25. Thus, when the basic waveform component isremoved from the read signal S, the second harmonic S2 can be extracted.As shown in portion (b) of FIG. 25, the waveform of the second harmonicS2 may be indicated by either the solid curve or dashed curve. That isto say, the second harmonic S2 may have its waveform indicated by eitherthe solid curve or the dashed curve depending on the wobble pattern ofthe wobble 238 b or 239 b.

The technique that has already been described with reference to FIG. 24is also applicable for use to distinguish the two types of secondharmonics S2 shown in portion (b) of FIG. 25 from each other.Specifically, a carrier signal (i.e., second sync signal) C2, which issynchronized with, and has the same frequency as, the second harmonicS2, is generated and multiplied by the second harmonic S2. And when theresultant multiplied signal S2×C2 is integrated for a predeterminedperiod of time, the information allocated to the given sub-block can bedefined either as “1” or as “0”.

More specifically, by getting the multiplication and integrationoperations performed by the multiplier 512 and integrator 513,respectively, as shown in FIG. 23, the address information recorded(i.e., “1” or “0”) can be detected by the heterodyne detection techniquein accordance with the phase of the second harmonic S2. The“predetermined period” herein refers to an interval in which a gatesignal G2 is asserted, i.e., an interval in which the sawtooth wobble238 b or 239 b is scanned by the read laser beam, as shown in FIGS. 21and 22. The gate signal G2 may be generated by the same technique as thegate signal G1.

As shown in FIG. 23, a ½ frequency divider 503 is preferably providedfor the feedback loop formed by the PLL 502. Then, the carrier signal C2having the twice higher frequency can be output from the PLL 502 to themultiplier 512 as well as to the input terminal of the frequency divider503.

FIGS. 21 and 22 each show the accumulated value AS associated with thesupplementary address information that has been obtained by the methoddescribed above and another accumulated value AM associated with theaddress information detection signal that has been recorded as thesawtooth wobble within the block. As shown in FIG. 23, the accumulatedvalues AS and AM are added together by an adder 520, thereby increasingthe SNR of the resultant integrated signal ACC. As a result, the addresscan be read correctly with much more certainty.

As shown in FIGS. 21 and 22, the integrated signal ACC is sampled andheld synchronously with the timing pulse SH and then the sampled andheld value is compared with a reference value GND, thereby defining theaddress information as “1” or “0”. The integrated signal ACC may besampled and held by the sample-and-hold circuit (S/H) 521 shown in FIG.23. And the sampled and held value may be compared with the referencevalue GND by the comparator 522 shown in FIG. 23.

It should be noted that the integrator 505 or 513 is reset at anappropriate timing (except the integration interval in which the gatesignal G1 or G2 is asserted), thereby resetting the integrated signalACC to zero (i.e., initial value).

In the preferred embodiment described above, time lags such as a groupof delays caused by the bandpass filters or circuit delay are totallyout of consideration. In an actual apparatus, however, its design shouldbe optimized with these time lags taken into account.

Also, in the preferred embodiment described above, each wobblerepresenting the address information has a sawtooth shape that ischaracterized by the gradient of its rising or falling displacements.Generally speaking, though, a “difference in shape” between twowaveforms having periodic repetitive patterns is created by thedifference in amplitude or phase between their harmonic components.Accordingly, as long as information can be recorded by utilizing the“difference in shape” between wobbles, the effects of the presentinvention are also achievable. That is to say, the present invention isnot limited to the sawtooth shapes described above. Nevertheless, thesawtooth shape is believed to be one of the most preferable wobbleshapes because the phase of a second harmonic, realizing a relativelygood SNR, changes remarkably in a sawtooth waveform.

Furthermore, in the preferred embodiment described above, after themultiplied signals have been integrated by the integrators 505 and 513,respectively, the resultant integrals are added together by the adder520 as shown in FIG. 23. However, since the integrators 505 and 513 aresupposed to add up the products obtained by the multiplier 504 and thoseobtained by the multiplier 512, respectively, the function of the adder520 may be incorporated into the integrator 505 or 513. For example, thefunctions of the integrators 505 and 513 and the adder 520 may beperformed by a single capacitor for receiving currents that have beensupplied from the multipliers 504 and 512.

Furthermore, in the preferred embodiment described above, themultipliers 504 and 512 are used to detect the phase of the addressinformation recorded. Alternatively, any other type of arithmetic orlogic elements may also be used as long as the phase information isdetectible. For example, a logic element such as an exclusive-OR (EXOR)gate for use in a PLL and other circuits may also be used to detect thephase of the address information.

In an optical disk medium according to various preferred embodiments ofthe present invention, an identification mark for use to identify asub-block (i.e., sub-block mark) is provided for each of a huge numberof sub-blocks (i.e., unit sections) that are arranged along the trackgroove. Thus, any sub-block can be detected easily. Particularly whenthe information “1” or “0” represented by the wobble of a portion of thetrack groove for a given sub-block is also represented by theidentification mark of the same sub-block, that information representedby the wobble of the sub-block can be read just as intended.

While the present invention has been described with respect to preferredembodiments thereof, it will be apparent to those skilled in the artthat the disclosed invention may be modified in numerous ways and mayassume many preferred embodiments other than those specificallydescribed above. Accordingly, it is intended by the appended claims tocover all modifications of the invention that fall within the truespirit and scope of the invention.

1. A recording apparatus for recording information in an optical diskmedium which comprises a track groove thereon and on which informationis recorded along the track groove on a block unit basis, the block unithaving a predetermined length, wherein the block unit includes a numberof sub-blocks that are arranged along the groove, wherein a sub-blockmark is provided wobbling in a sine wave curve within each saidsub-block and used to identify the sub-block, and wherein a part of thetrack groove has a sawtooth-like wobble shape that is defined by acombination of a steep displacement pattern and a gentle displacementpattern to represent address information of the block unit, wherein thesub-block mark is formed by locally changing the phase of the sine waveand wobble.
 2. The recording apparatus of claim 1, wherein theinformation on the optical medium represented by the wobble shape of thetrack groove is also represented by the sub-block mark.
 3. A recordingapparatus for recording information in an optical disk medium whichcomprises a track groove thereon and on which information is recordedalong the track groove on a block unit basis, the block unit having apredetermined length, wherein the block unit includes a number ofsub-blocks that are arranged along the groove, wherein a sub-block markis provided wobbling in a sine wave curve within each said sub-block andused to identify the sub-block, and wherein a part of the track groovehas a sawtooth-like wobble shape that is defined by a combination of asteep displacement pattern and a gentle displacement pattern, andwherein the sub-block mark is formed by locally changing the phase ofthe sine wave and wobble, comprising: a first phase detector whichdetects phase polarity of a reproduced sub-block mark signal; and asecond phase detector which detects phase polarity of a reproducedsawtooth-like wobble signal, wherein the detected phase polarity of thereproduced sub-block mark signal and the detected phase polarity of thereproduced sawtooth-like wobble signal determine address information. 4.An optical disk medium which comprises a track groove thereon and onwhich information is recorded along the track groove on a block unitbasis, the block unit having a predetermined length, wherein the blockunit includes a number of sub-blocks that are arranged along the groove,wherein a sub-block mark is provided wobbling in a sine wave curvehaving a basic frequency within each sub-block and used to identify thesub-block, and wherein a part of the track groove has a sawtooth-likewobble shape that is defined by a phase polarity of a second harmonic ofthe basic frequency to represent address information of the block unit,wherein the sub-block mark is formed by locally changing the phasepolarity of the sine wave wobble.
 5. The optical disk medium of claim 4,wherein the phase polarity of the second harmonic is inverted or notinverted depending on whether the address information is “1” or “0”. 6.The optical disk medium of claim 4, wherein the information representedby the wobble shape of the track groove is also represented by thesub-block mark.
 7. A recording apparatus for recording information in anoptical disk medium which comprises a track groove thereon and on whichinformation is recorded along the track groove on a block unit basis,the block unit having a predetermined length, wherein the block unitincludes a number of sub-blocks that are arranged along the groove,wherein a sub-block mark is provided wobbling in a sine wave curvehaving a basic frequency within each sub-block and used to identify thesub-block, and wherein a part of the track groove has a sawtooth-likewobble shape that is defined by a phase polarity of a second harmonic ofthe basic frequency to represent address information of the block unit,wherein the sub-block mark is formed by locally changing the phasepolarity of the sine wave wobble.
 8. A recording apparatus of claim 7,wherein the phase polarity of the second harmonic is inverted or notdepending on whether the address information is “1” or “0”.
 9. Areproducing apparatus for reproducing information in an optical diskmedium which comprises a track groove thereon and on which informationis recorded along the track groove on a block unit basis, the block unithaving a predetermined length, wherein the block unit includes a numberof sub-blocks that are arranged along the groove, wherein a sub-blockmark is provided wobbling in a sine wave curve having a basic frequencywithin each sub-block and used to identify the sub-block, and wherein apart of the track groove has a sawtooth-like wobble shape that isdefined by a phase polarity of a second harmonic of the basic frequencyto represent address information of the block unit, wherein thesub-block mark is formed by locally changing the phase polarity of thesine wave wobble.
 10. A reproducing apparatus of claim 9, wherein thephase polarity of the second harmonic is inverted or not depending onwhether the address information is “1” or “0”.
 11. A reproducing methodfor reproducing information in an optical disk medium which comprises atrack groove thereon and on which information is recorded along thetrack groove on a block unit basis, the block unit having apredetermined length, wherein the block unit includes a number ofsub-blocks that are arranged along the groove, wherein a sub-block markis provided wobbling in a sine wave curve having a basic frequencywithin each sub-block and used to identify the sub-block, and wherein apart of the track groove has a sawtooth-like wobble shape, including thesteps of: detecting locally changed phase polarity of the sine wavewobble: and detecting a phase polarity of a second harmonic of thesawtooth-like wobble.
 12. An optical disk recording apparatus forrecording one or more blocks of information on a track groove of anoptical disk medium; wherein signals of a particular pattern arerecorded in a leading part and a following part of data signals in eachblock on the track groove, wherein a block mark is provided on theoptical disk for indicating a position that each block of information isrecorded by wobbling at least a part of the track groove in a sine wavecurve, and both a beginning position of the leading part and a finishingposition of the following part of the data signals are recorded in anarea distant from the block mark by 10 μm or more.
 13. The optical diskrecording apparatus according to claim 12, wherein the block mark on theoptical disk includes locally changing the phase of the sine wavewobble.
 14. The optical disk recording apparatus according to claim 12,wherein the block mark on the optical disk is provided with a sinewobble having a frequency different from that of the other parts of thetrack groove.
 15. The optical disk recording apparatus according toclaim 13, wherein a part of the track groove has a sawtooth-like wobbleshape that is defined by a combination of a steep displacement patternand a gentle displacement pattern to represent address information ofthe block unit.
 16. An optical disk medium on a track groove of whichrecorded one or more blocks of information; wherein signals of aparticular pattern are recorded in a leading part and a following partof data signals in each block on the track groove, wherein a block markis provided on the track groove for indicating a position that eachblock of information is recorded by wobbling at least a part of thetrack groove in a sine wave curve, and both a beginning position of theleading part and a finishing position of the following part of the datasignals are recorded in an area distant from 10 μm or more from theblock mark.
 17. The optical disk medium according to claim 16, whereinthe block mark on the optical disk includes locally changing the phaseof the sine wave wobble.
 18. The optical disk medium according to claim16, wherein the block mark on the optical disk is provided with a sinewobble having a frequency different from that of the other parts of thetrack groove.
 19. The optical disk medium according to claim 17, whereina part of the track groove has a sawtooth-like wobble shape that isdefined by a combination of a steep displacement pattern and a gentledisplacement pattern to represent address information of the block unit.